From an intellectual law perspective WordPress owns the template and all the associated ‘tools’ for ‘us’ to create and use the blog. As far as who owns the material that we users populate into that WordPress template belongs to the true owner. This can be you the user, as the original creator or author, or that that you purchased to put on the blog eg. photographs, videos, music files, exerts from books etc.
To protect your own intellectual property and acknowledge the intellectual property that you either purchased or received written permission from others (photographs, videos, music files, exerts from books) simply add a ‘legals’ page to your blog saying so.